#include <bits/stdc++.h>

using namespace std;

int main()
{
    long long n, s;
    cin >> n >> s;
    vector<int> a(n);

    for (int i = 0; i < n; i++)
    {
        cin >> a[i];
    }

    sort(a.begin(), a.end());

    long double avg = s * 1.0 / n, cur_avg = avg, tmp = 0;
    for (int i = 0; i < n; i++)
    {
        if (a[i] < cur_avg)
        {
            s -= a[i];
            tmp += (avg - a[i]) * (avg - a[i]);
            cur_avg = (s * 1.0) / (n - 1 - i);
        }
        else tmp += (cur_avg - avg) * (cur_avg - avg);
    }

    printf("%.4Lf", sqrt(tmp / n));
    return 0;
}